Day/night cycle even more important to life than previously suspected

It makes a lot of sense that most living organisms have physiological cycles that are in sync with the Earth’s rotation, in view of the importance of sunlight for activity and metabolism of the organism. That’s what the circadian cycle is all about. Even the expression levels of various genes in an organism’s cells is in sync with this cycle.

Not all organisms, however, have an obvious dependence on the 24-hour cycle. Some, like mussels, live in environments between the land and the sea, and thus experience changes based on tidal ebb and flow – roughly twice every day. Mussels even close their shells when receding tides leave them exposed to the air.

Yet even so, their gene expression cycle remains in sync not with the tides, but with the same 24-hour circadian cycle as most of the rest of the biological world.

Day/night cycle even more important to life than previously suspected

Researchers at USC were surprised recently to discover just how much the rising and setting of the sun drives life on Earth – even in unexpected places.

Their findings, which appear this month in the Proceedings of the National Academy of Sciences, “speak volumes to the evolution of life on Earth,” according to USC scientist Andrew Y. Gracey.

“Everything is tied to the rotation of the planet,” he said.

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